The present invention relates to a method for recording and reproducing a video format signal, and more particularly to a system for recording and reproducing video and audio information as a video format signal on and from a recording medium.
For recording audio information accompanying video information on a recording medium at the same time the video information is recorded, there is known a method of inserting the audio information on a compressed time basis in a portion of a video format signal, and inserting the video information in the remainder of the video format signal. The audio information is recorded in a digitized form. More particularly, one sampled value of the digitized audio information is expressed by a prescribed number of bits constituting one word which is recorded. In reproducing the recorded information from the recording medium, it is necessary to achieve data word synchronization and clock (bit) synchronization when demodulating the video format signal.
Further, for recording audio information accompanying video information on a recording medium at the same time the video information is recorded, there is known a method of inserting the audio information on a compressed time basis in a portion of a video format signal, and inserting the video information in the remainder of the video format signal. With such a conventional method, the audio and video information is inserted in fixed patterns in the video format signal, and the video format signal is generated by the following processing: The analog audio signal is converted into a digital signal by a modulation process of high compression capability such as ADM (Adaptive Delta Modulation). The produced digital signal is interleaved or rearranged on a time basis, and thereafter a redundancy bit serving as an error correcting code which is completed in each block is added to the digital signal. The digital signal with the error correcting code added is then written at a sampling frequency f.sub.1 into a buffer memory which compresses the signal on a time basis. The stored digital signal is thereafter read out of the buffer memory at a frequency f.sub.2 higher than the frequency f.sub.1 to thereby compress the audio information. The digital data including the audio information, and control data such as a digital start code indicative of a position wherein the digital data starts to be inserted, a stop code for commanding reproduction of a still image, and data count data representative of the amount of digital data are inserted into a desired block. Video information may sometimes be inserted in remaining blocks.
The video format signal thus produced is recorded on a recording medium, and the recorded information will be reproduced from the recording medium by a reproducing system. FIG. 1 of the accompanying drawings illustrates a sound adding device in such a reproducing system for adding sound to a still image obtained by an information readout device after the compressed audio information has been gained by the information readout device.
As shown in FIG. 1, a video format signal (FIG. 2) produced by a video disc player (not shown) serving as the information readout device is supplied through a video output terminal to an image reproducing device (not shown) and also to a signal separator 111. The signal separator 111 separates from the video format signal audio data composed of digital data including audio information, control data, and a synchronizing signal. The synchronizing signal issued from the signal separator 111 is supplied to a timing signal generator 112. The sound digital data issued from the signal separator 111 is supplied to a large-capacity buffer memory 113. The control data issued from the signal separator 101 is fed to a digital data start detector 114, a data count latch 115, and a stop code detector 116. The digital data start detector 114 generates a pulse when it detects a digital start code from the control data. The pulse from the digital data start detector 114 is supplied to a set terminal of a flip-flop 117, which produces a Q output of logic "1" in response to the pulse applied to the set terminal and a Q output of logic "0" in response to a pulse applied to a reset terminal thereof. Therefore, when the digital start code is detected, the Q output of logic "1" is produced by the flip-flop 117 and supplied as a write flag signal to an input terminal of an AND gate 119. The stop code detector 116 generates a pulse when it detects a stop code from the control data. The pulse issued from the stop code detector 116 is supplied to a set terminal of a flip-flop 118. Therefore, when a stop code is detected, the Q output of the flip-flop 118 becomes a logic "1" and is supplied as a readout flag signal to an input terminal of an AND gate 120. The data count latch 115 serves to store and hold data count data in the control data.
When data is to be written into or read out of the buffer memory 113, an address input terminal thereof is supplied with an output signal from an address counter 121 which specifies storage positions. The address counter 121 is a binary counter which counts upwardly in response to rising edges of pulses supplied to a clock input terminal thereof, and which holds an initial condition while a logic "1" is applied to a clear input terminal. The output signal from the address counter 121 is also supplied to an input terminal of a coincidence detector 122, the other input of which is supplied with an output from the data count latch 115. The coincidence detector 122 compares the output from the data count latch 115 with the output from the address counter 121, and issues a pulse when the compared outputs coincide with each other. The pulse from the coincidence detector 122 is supplied to reset terminals of the flip flops 117 and 118. Therefore, when all audio data separated by the signal separator 111 is supplied to the buffer memory 113, or all audio data is read out of the buffer memory 113, the Q outputs of the flip-flops 117 and 118 become a logic "0".
The other input terminals of the AND gates 119 and 120 are supplied with two pulse signals having different repetitive frequencies from the timing signal generator 112. The timing signal generator 112 produces such two pulse signals based on the snychronizing signal fed thereto. When the Q output of the flip-flop 117 is a logic "1" or the write flag is ON, one of the output pulse signals from the timing signal generator 112 is passed by the AND gate 119 to be supplied as write pulses f.sub.2 (W) to the buffer memory 113. When the Q output of the flip-flop 118 is a logic "1" or the readout flag is ON, the other output pulse signal from the timing signal generator 112 is passed by the AND gate 120 to be supplied as readout pulses f.sub.1 (R) to the buffer memory 113. The repetitive frequency of the write pulse signal f.sub.2 (W) is higher than that of the readout pulse signal f.sub.1 (R) to expand the compressed audio information. The write and readout pulse signals f.sub.2 (W) and f.sub.1 (R) issued from the AND gates 119 and 120 are supplied as inputs to a NOR gate 123, which issues an output to the clock input terminal of the address counter 121. When the buffer memory 113 is in a write mode in response to the write pulse signal f.sub.2 (W) supplied thereto, the address counter 121 counts up a pulse to successively change the specified storage position each time the audio data is written. Likewise, when the buffer memory 113 is in a readout mode in response to the readout pulse signal f.sub.1 (R) supplied thereto, the address counter 121 counts up a pulse to successively change the specified storage position each time the audio data is read out. The clear input terminal of the address counter 121 is fed with pulses supplied through an OR gate 124 from the digital data start detector 114 and the stop code detector 116, thereby initializing the address counter 121. Accordingly, when a digital start code is detected, audio data items are successively stored into storage positions in the buffer memory 113 which start from the storage position corresponding to the initial value of the address counter 121. When a stop code is detected, audio data items are successively read out of storage positions in the buffer memory 113, which start from the storage position corresponding to the initial value of the address counter 121.
The audio data as read out of the buffer memory 113 is corrected by an error correcting circuit 125, and the corrected audio data is supplied to a deinterleaver 126. The deinterleaver 126 rearranges the audio data into an original series of data items, which are then supplied to a D/A (digital-to-analog) converter 127, with its clock input terminal supplied with the readout pulse signal f.sub.1 (R). The D/A converter 127 stores the input data in response to the readout pulses f.sub.1 (R), and thereafter generates a voltage having a level corresponding to the input data. The D/A converter 127 thus issues an analog audio output to an audio playback device (not shown).
The output pulse from the stop code detector 16 is supplied to a player controller 128 which is also supplied with a play command signal generated in response to depression of a play switch (not shown). The player controller 128 generates control signals to reproduce a still image when the pulse is issued from the stop code detector 116 and a moving image when the play command signal is produced, and supplies such control signals to a video disc player (not shown).
When a digital start code and data count data are issued from the video disc player in advance of audio data recorded in a sound recording frame F.sub.1 extending over a plurality of frames, the flip-flop 117 is set to turn on the write flag and initialize the address counter 121. At the same time, data count data is stored and held in the data count latch 115. Audio data in the amount indicated by the data count data is then written into the buffer memory 113. Thereafter, when a stop code is issued prior to video information recorded in an image recording frame F.sub.2, a still image is reproduced and simultaneously the flip-flop 118 is set to turn on the readout flag, whereupon the audio data is read out of the buffer memory 113 to add sound to the still image. After all of the audio data has been fully read out of the buffer memory 113 to finish the sound reproduction, the PLAY switch or the like is manually operated to disable the still image reproduction, and the above operation can then be repeated.
With the reproducing system including the sound adding device according to the conventional recording and reproducing system, audio data corresponding to one still image is first all written into the buffer memory, and then the still image is reproduced and at the same time the written audio data is read out to generate reproduced sound. After all written audio data items have been fully read out, a next cycle of operation is started. Therefore, reproduced sounds based on audio data accompanying a plurality of still images cannot successively be generated, and hence it has not been possible to effect a mode in which still images are successively switched on while reproducing music recorded as audio data. The buffer memory is required to have a capacity large enough to store all audio data items corresponding to a single still image, with the result that the circuit arrangement of the reproducing system is undesirably large.
Still further, for recording audio information accompanying video information on a recording medium at the same time the video information is recorded, there is known a method of inserting the audio information on a compressed time base in a portion of a video format signal, and inserting the video information in the remainder of the video format signal. With such a method, it is necessary to identify the audio and video information on a reproducing side, and process reproduced signals dependent on the information.
Moreover, for recording audio information accompanying video information on a recording medium at the same time the video information is recorded, there is known a method of inserting the audio information on a compressed time base in a portion of a video format signal, and inserting the video information in the remainder of the video format signal. Since the narration for a still image is recorded as a compressed form, the narration is representative of sound continued for about 10 seconds for one still image. Therefore, the method has been limited to use as a so-called automatic projector.